The proposed program of research aims to explore three interrelated problems concerning the development of the child's understanding of objects and events. First is a longitudinal study of early language comprehension beginning in the period before the child starts to talk. The purpose is to investigate what words and syntactic expressions the child responds to systematically, and to examine the concepts encoded by these words and expressions. Second is a series of studies of the development of conceptual organization. The purpose of these studies is to determine how the child's different concepts are organized, and whether the nature of this organization changes during development. The studies use mutual facilitation and interference in memory for words as an index of the organization of the concepts encoded by these words. This approach has currently been adopted in research with adults. The proposed studies modify and extend this methodology for use with the young child. Third is a series of studies of the child's inferential abilities. The proposed studies are concerned with spatial reasoning. The aim is to clarify the development of the mental processes involved in the child's ability to obtain information about events through deductive inference.